The present invention generally relates to wireless communication networks, and particularly relates to reverse link rate control in such networks.
Interference limits reverse link capacity in Code Division Multiple Access (CDMA) networks, meaning that the number of mobile stations simultaneously transmitting to a given network base station or stations is limited by the resultant overall interference at the base station receivers. CDMA networks typically employ closed loop power control on the reverse link, wherein the network base stations adjust the transmit power of each mobile station up or down as needed to receive the mobile station's transmitted signals at a targeted signal quality. Such control prevents any individual mobile station from transmitting at a higher-than-necessary power and thus helps to reduce that mobile station's contribution to the overall interference.
By working to reduce the interference caused by each mobile station, the network more efficiently uses its reverse link capacity, which is a measure of the overall loading that can be supported by the base station. For example, reducing the interference contribution of each mobile station increases the number of simultaneous users that can be supported at a target reverse link loading, and/or allows one or more of those users to operate at higher reverse link data rates than otherwise could be permitted. That latter benefit touches on the point that higher data rates require higher target received signal qualities and thus require greater mobile station transmit power than do lower data rates under the same radio conditions.
The relationship between data rates and required transmit power plays into the evolving wireless network standards that define multiple reverse link data rates, thereby allowing base stations to control overall reverse link loading based at least in part on controlling the assigned reverse link data rates of individual mobile stations. For example, if it is desirable to support a greater number of simultaneous users, some or all of the users could be forced to lower data rates to thereby reduce the individual interference contribution of those users. Similarly, the base station may schedule which users transmit on the reverse link in each of a succession of scheduling intervals. By limiting the number of simultaneous users in each interval, overall interference is kept within tolerable levels. The forthcoming “Release D” of the IS-2000 standard exemplifies this type of rate-adjustable reverse link interface, but other network standards define at least broadly similar rate adjustable reverse link channels that can be managed by the network.